Abstract: A basic structure of a reference voltage generation circuit is formed by a buffer amplifier (21) and a resistive element (22) without using a band gap regulator. Thus, an influence of a noise of the band gap regulator as in the conventional art is eliminated. There are provided comparators (23) and (24) for comparing an input voltage of the buffer amplifier (21) with an output voltage of a band gap regulator (10), and a control circuit (25) for variably controlling a resistance value of the resistive element (22) in response to comparison signals. Consequently, even if an output voltage (Vout) of the buffer amplifier (21) temporarily fluctuates with a change in a source voltage (VDD), it returns into a desirable voltage range and converges through a variable control of the resistance value.

Abstract: There are provided a coefficient ROM 1 for storing coefficients representing angular frequencies corresponding to a desired frequency and a sampling frequency, that is, two types of coefficients for a single desired frequency, an accumulated addition calculating portion 2 for using one of the coefficients until an accumulated addition value does not exceed a threshold and using the other coefficient when the accumulated addition value exceeds the threshold, thereby adding coefficient values stored in the coefficient ROM 1 every sampling frequency sequentially to obtain an angular frequency for each sample point, and a CORDIC 3 for calculating an amplitude of a sinusoidal wave corresponding to the angular frequency for each sample point which is obtained by the accumulated addition calculating portion 2, thereby generating a sinusoidal wave signal having a desired frequency, and the sinusoidal wave signal having the desired frequency can be generated by a digital calculation from only the two types of coeffici

Abstract: Signal lines (13) and (14) to be used for supplying a signal between an analog circuit and a digital circuit are provided in different regions from power-ground lines (11) and (12) to be used for supplying a power to the analog circuit and the digital circuit in such a manner that the signal lines (13) and (14) do not cross the power-ground lines (11) and (12). For example, the power-ground lines (11) and (12) are provided along an outer periphery of a semiconductor chip (10) and the analog circuit and the digital circuit are disposed on the inside of the power-ground lines (11) and (12), and the signal lines (13) and (14) are provided between the analog circuit and the digital circuit.

Abstract: An original filter is connected to an adjustment filter in the longitudinal way. The original filter has a first filter coefficient of a symmetric numeric string. The adjustment filter has a contact point at a position where the maximum value is acquired in the original filter frequency amplitude characteristic A and has a symmetric second filter coefficient realizing the frequency amplitude characteristic B having the minimum value at the contact point. By executing a convolution calculation of the first filter coefficient and the second filter coefficient, it is possible to design a desired filter coefficient.

Abstract: There are provided a BPF (15) for extracting an image frequency component from a modulating signal generated by modulating I and Q signals through a quadrature modulating portion (3), an energy detecting portion (16) for detecting an energy of the image frequency component, and an amplitude correcting portion (12) and a phase correcting portion (13) which correct an amplitude and a phase of the I signal to minimize the detected energy. By correcting the amplitude and the phase to minimize the energy of the image frequency component contained in the generated modulating signal without detecting amplitude and phase errors themselves of the I and Q signals, it is possible to accurately correct the amplitude and phase errors of the I and Q signals without an influence of a limit of precision in an error detection.

Abstract: A JFET 4 to be an antenna buffer for an AM broadcasting signal is constituted in a source follower form of a 100% negative feedback type, and a tuning circuit including a variable capacitive circuit 7 and a transformer 6 is provided in a subsequent stage to the JFET 4 and an amplifying circuit including MOSFETs 10 and 11 is provided in a further subsequent stage thereto. Consequently, it is possible to reduce a signal distortion rate in the JFET 4 and to eliminate a drawback that every frequency component enters the amplifying circuit to saturate the amplifying circuit, resulting in an occurrence of a distortion in an output signal. By switching a plurality of capacitors CT1, CT2, . . . CTn to cause a capacitance value to be variable without using a varactor diode, it is possible to integrate the capacitors CT1, CT2, . . . CTn in an IC 20.

Abstract: By providing switch portions (8a) and (8b) for switching I and Q signals and outputting them to a single A/D converter (9), and sequentially converting the I and Q signals output from the switch portions (8a) and (8b) into digital signals by the A/D converter (9) and supplying them to a DSP (10), it is possible to carry out an A/D conversion processing for the I and Q signals through the same A/D converter (9). Consequently, it is possible to eliminate a drawback that an amplitude error or a phase error is made between the I and Q signals due to a variation in an A/D converting characteristic.

Abstract: A first-stage amplifier of an AM receiving circuit is built into an IC 2 as a differential amplifying circuit 3. The differential amplifying circuit 3 is connected to one pad P1 of the IC 2. Then, a high pass filter is configured by connecting a resistor Ra between two input terminals of the differential amplifying circuit 3 and connecting a capacitor Ca between the resistor Ra and ground and in series with the resistor Ra and ground. Thus, the resistor Ra and capacitor Ca integrated into the IC 2 allows hum noise to be removed.

Abstract: In a mixer circuit 6 connected in common to output sides of an LNA 2 for FM receiving and an LNA 4 for AM receiving, each of a radiofrequency signal output from the LNA 2 for FM receiving and a radiofrequency signal output from the LNA 4 for AM receiving is frequency-converted into an intermediate frequency signal of a lower intermediate frequency for AM broadcast waves. In this way, receiving of an FM broadcast is performed by a low IF system and receiving of an AM broadcast is performed by a single conversion system; the need for separately providing a mixer circuit, a local oscillation circuit and an IF filter for down-mixing of AM broadcast waves is eliminated.